1. Field of the Invention
This invention relates generally to shaft couplings having parallel transition and direct clutches and, more particularly, to an improvement in spline type direct clutches for such couplings.
2. Description of the Prior Art
In a lift/cruise aircraft, a gas turbine engine prime mover on the aircraft develops shaft horsepower to rotate a rotor during vertical lift and shaft horsepower or thrust to propel the aircraft during horizontal cruise. When the rotor is rotating, it is desirable to effect a direct connection, as by splines, between the engine and the rotor. During cruise, when the rotor is stationary, the latter must be completely disconnected from the engine. During transitions between lift and cruise, relative rotation between the rotor and the engine takes place as the rotor transitions between rest and a synchronous speed relative to a power supply shaft from the engine. One coupling proposed for such applications and disclosed in U. S. Pat. No. 4,157,135, issued June 5, 1979 to Devlin and Janneck and assigned to the assignee of this invention, includes a hydraulically actuated friction type transition clutch and a hydraulically actuated direct clutch wherein a spline connection may be established and severed when the rotor is at a synchronous speed relative to a power supply shaft from the engine. A coupling according to this invention includes a spline type direct clutch having an improved withdrawal characteristic relative to heretofore known spline clutches.